Patent GB-855675-A (GB)
Title: Improvements in or relating to thermo-responsive electrical switches
Inventor: SCHMIDINGER JOSEPH
IPC: H01H61/06
Filed: 1958-05-21
Abstract: 855,675. Thermal switches. TUNG-SOL ELECTRIC Inc. May 21, 1958, No. 16271/58. Class 38 (5). [Also in Group XXXVIII] A thermally-expansible strip is secured at one end to a metallic structure which carries a two-position metallic movable contactmember biased toward one position and is secured at the other end under tension to said movable member such that when cold the strip holds the member in its other position against the bias; an electrical connection is made on the strip intermediate its ends whereby current passing in the two parts in parallel may heat the strip and allow the movable member to move to its first position. Three embodiments are described wherein snap-action is provided respectively by magnetic means, a bowed spring-blade and by a trifurcated blade arrangement. In the first embodiment an insulating base 2 carries a magnetizable plate 18 shaped as shown in Figs. 1 and 2. A fixed contact 32 is carried on an adjustable tongue pressed up from a plate 28 which is insulated from plate 18 but connected by a rivet 14 to a terminal 8. An armature 24 carries a moving contact 34 which is biased away from contact 32 by the spring mounting 22. A thermally-expansible strip 26 is anchored to a lug 18c on plate 18 and attached under tension to the spring 22 to hold contacts 32, 34 closed. Lug 18c may be bent to adjust the tension in strip 26. A coil 20 on plate 18 is connected to a terminal 4 and to the middle of strip 26. Current can thus flow from terminal 4 via coil 20, strip 26, plate 18 and armature 24, contacts 34 and 32 to terminal 8. When strip 26 is sufficiently heated it expands to allow armature 24 to snap open, breaking the circuit, which is reclosed when the strip 26 cools. A bracket 36 has a part bent over armature 24 to provide a back-stop and is connected to a terminal 6. In the embodiment of Fig. 6 the base of the switch is formed by a channel-like frame 48 clamped around insulation 50 and terminal members 68 and 64. Member 64 is bent, as shown, to carry a contact 66 within a hole 52 in frame 48, and a bowed spring 56 carries a co-operating contact 54. Strip 58, anchored on lug 60, is attached under tension to a bracket 62 on spring 56 and has an electrical connection 70 to terminal 68. When cold strip 58 constrains spring 56 to the shape shown by the full lines, wherein contacts 66, 54 are closed, but when strip 58 expands due to current therethrough the spring 56 snaps to its bowed position, shown by broken lines, and contacts 66, 54 open. The end of terminal 64 protrudes downwardly to provide a means of adjusting contact 66. In the embodiment shown in Fig. 8 a metal frame 90 is bent around insulation 96 to clamp terminal members 92 and 94. Member 92 carries a fixed contact 84 and a back-stop 83 for co-operation, respectively, with a contact 81 and insulated button 82 carried on a snap-plate comprising three metal strips interconnected at their ends and fixed at 98 to frame 90. The outer strips 79 are in tension and the centre strip 80 is bowed upwardly. Expansible strip 88 is attached to a lug 104 on frame 90 and to a bracket 86 secured to bowed strip 80. When cold, the strip 88 causes strip 80 to flex, as shown, and hold button 82 against stop 83. When the strip 88 is heated by current via conductor 106 it allows strip 80 to snap upwards and close contacts 81 and 84. Tension in strip 88 is adjustable by bending lug 104 and contact 84 is adjustable by an extension 92b of member 92.